This invention relates to object recognition systems; and more particularly, it relates to methods of compensating for pixel histogram distortion which can occur in such systems.
One particular use for the present invention is in object recognition systems which either grant or deny a person access to a secure area based on whether or not an image from a camera of the person's face is recognized by the system. Also, the present invention can be used in object recognition systems which employ a robotic arm to select or reject a component based on whether or not an image from a camera of the component is recognized by the system.
In all of the above applications, a key task which needs to be performed as part of the recognition process is that two images must be correlated. One of these images is the image, from a camera, of an unknown object which the system is trying to recognize; and the other image is of a known object which is stored in the system as a reference. If the correlation between the two images exceeds a predetermined threshold value, then the unknown object is recognized.
However before the two images are correlated, it is highly desirable to adjust the magnification of the image of the unknown object such that it is closely matches the magnification of the reference. This is because as the difference in magnification of the unknown object and the reference increases, their correlation decreases; and that will cause recognition errors.
In the case where a person is seeking access to a secure area, the magnification of that person's image from the camera will increase as the person stands closer to the camera, and vice-versa. Such variations in magnification will occur in a work environment because it is not practical for a person to stand exactly the same distance from the camera each time access is sought.
Before any adjustment in magnification is made to the image of the unknown object, the current magnification of that object must be detected. This can be attempted by sensing the width of the unknown object in the image from the camera and comparing it to the width of the reference.
However, the present inventor has found that under certain conditions, a histogram of the pixels in the image from the camera can be distorted in a particular fashion which causes errors to occur when the width of the unknown object is sensed. If that happens, the magnification of the image from the camera will be adjusted incorrectly, and thus a recognition error will occur.
Accordingly, a primary object of the present invention is to provide an object recognition system in which the above problem is overcome.